1. Field of the Invention
The present invention relates to novel fluorine-containing aromatic ether bis-imides, useful in the preparation of thermosetting resins.
2. Description of the Prior Art
Thermosetting resins having a structure based on imide linkages are used in industry for applications based on their advantageous properties, such as electrical insulation, thermal stability, and dimensional stability of molded articles. These addition-type polyimides are cross-linked polymers which may be prepared from bis-imides which are functionalized with unsaturated end groups, such as norbornenyl or ethynyl, capable of undergoing thermal polymerization to form a highly cross-linked polyimide. The polymers thus formed are thermoset and cannot be reprocessed by heat and pressure. Resins of this type are used in a variety of applications including, for example, impregnation varnish, molded articles or components, laminated boards, electronic circuit board manufacture, adhesives, etc. The importance of the various properties of the resin will vary depending on the end application for which it is intended, and the properties of a particular resin will depend, in part, on the elemental composition and structure of the bis-imide monomers employed. The fluorinated bis-imides of this invention are well-suited for use as monomers for the preparation of addition-type polyimides.
One important advantage of polyimides based on the fluorinated bismaleimides and bisnadimides of this invention is that of improved electrical properties. In particular, these polymers are useful as dielectric layers in microelectronic applications. The dielectric constant (measured by ASTM D 150-87) of a polyimide is the ratio of the capacitance of a capacitor containing the polyimide to the capacitance of the same electrode system with air replacing the insulation. Low dielectric values are preferred as this allows for increased circuit density and high speed-high frequency operation in the high megahertz region.
Another important property is moisture absorption which is a measure of the amount of moisture a polymer absorbs from the air at different humidities. Incorporation of fluorinated bismaleimides and bisnadimides of this invention lowers the moisture absorption of the polymer. A lower moisture absorption is important since the amount of moisture on a material has a strong effect on its electrical properties, such as the dielectric constant and the dissipation factor. In addition, a low moisture regain gives rise to other useful properties such as hydrolytic stability and greater resistance to caustic. This permits use of the polymers over a wider range of environmental conditions.
Another property of polymers incorporating the fluorinated monomers of this invention is high optical transparency. Polyimides incorporating these monomers are nearly transparent to slightly yellow in appearance and, as a result, are particularly useful for optical applications. Incorporation of fluorinated alkyl side chains in the backbone of the bis-imide moiety of these polyimides is responsible for increased optical transparency. Polyimides incorporating these monomers are less flammable due to the inclusion of the fluorinated bismaleimide and bisnadimide monomers of this invention.
Polyimides incorporating these fluorinated bisnadimide and bismaleimide monomers do not lose the usual useful properties typically associated with polyimides such as high thermal stability and excellent mechanical properties.